By catalyzing hydrolysis of cAMP and cGMP, cyclic nucleotide phosphodiesterases (PDEs) are critical regulators of intracellular concentrations of, and biological responses mediated by, cyclic nucleotides, including immune/inflammatory responses. Understanding cellular regulation of PDE isoforms [which belong to ten gene families (PDE1-10)] will be of increasing importance for targeting specific PDEs in treating pulmonary disorders. Although individual cells usually contain representatives of several PDE gene families, little is known of signalling pathways involved in cytokine and growth factor regulation of different PDEs in a single cell. In murine FDCP2 promyeloid cells, IL-4 and IGF-1 activate PDE3 and PDE4, whereas IL-3 activates only PDE4. Studies with TNFalpha and inhibitors of JAK, PI3- K, PKC, and MAPK kinases indicate that both IGF-1 and IL-3 activate PDE3 and PDE4 via PI3-K-dependent signals. Downstream of PI3-K, regulatory pathways diverge; PDE4, but not PDE3, is activated by MEK/MAPK-dependent signals. FDCP2 cells were, therefore, permanently transfected with wild type (wt), constitutively active (CA), or kinase inactive (KI) forms of MEK and PKB. Studies with these transfected cells indicated that PDE4 was activated by MEK/MAPK-dependent signals, and that PDE3 was phosphorylated and activated by PKB-dependent signals. Recombinant mouse (M) PDE3B was phosphorylated and activated in vitro by PKB; a truncated MPDE3B mutant lacking consensus PKB phosphorylation sites was not phosphorylated/activated. In cells expressing WT PKB, the proapoptotic protein BAD was phosphorylated in response to IGF-1; phosphorylation was blocked by 8-Br-cAMP or the PDE3 inhibitor cilostamide. These and other data suggest that PDE3B is a downstream target, if not substrate, of PKB and may function as an effector of PKB in regulation of cAMP pools that modulate, at least in part, effects of PKB on survival/proliferation of FDCP2 cells. - PDE3, PDE4, cyclic nucleotide hydrolysis, insulin, IGF-1, Protein Kinase B, FDCP2 hematopoietic cells, cell survival/proliferation